Keratin is a family of fibrous structural proteins, and is the key structural material making up the outer layer of skin and also the hair and nails. Keratin proteins contain a large amount of cysteine (Cys) (approximately 14%). As keratinized cells are constantly being shed and replaced, it is important that the body have a large pool of bioavailable Cys for protein synthesis.
Cys is considered a non-essential amino acid, but in some cases, such as in infants, the elderly, and individuals with certain metabolic diseases or malabsorption syndrome, it may be considered essential. It is readily available in many high protein foods, including meats, but this may be problematic for those who do not consume meat. In some regions it can be added as a food additive (E number is E920). However, such additives are generally not favored by consumers, and many regulatory agencies either limit or do not allow amino acids to be added to food.
A hydrolyzed hen's egg lysozyme is described in WO 2008/052995 (DSM IP ASSETS BV; which is hereby incorporated herein by reference) which has a Trp/Large Neutral Amino Acid (“LNAA”) ratio of more than 0.15, wherein LNAAs are the sum of the phenylalanine, leucine, isoleucine and valine in the plasma. Many of the hydrolyzed peptides are di- or tri-peptides containing Trp. A commercial product form of this lysozyme hydrolysate is available from DSM Nutritional Products under the name “LumiVida”. The lysozyme hydrolysate has been shown to be beneficial for a number of aspects including improving mood and cognition.
It would be desirable to make Cys which has been ingested more bioavailable in order to benefit keratin containing tissues, such as the skin, nails, and hair.